The present invention relates to a carrier used in a two-component developing method, in particular a carrier coated with polyolefinic resins.
A two-component developing method, in which insulating nonmagnetic toner particles are mixed with carrier particles to be frictionally charged and these particles are carried and brought into contact with electrostatic latent images to develop electrostatic latent images, has been known as an electrostatic latent image-developing method.
The carrier particles used in such the two-component developing method have been usually coated with suitable materials on account of reasons such as the prevention of toners from forming films on surfaces of carrier particles, the formation of a surface having uniform properties, the prevention of surface oxidation, the prevention of reduced resistance to humidity, the prolongation of useful life time of developers, the protection of a photosensitive member from damages or abrasion by carriers, the control of chargeable polarity and the control of a charging quantity.
Polyolefinic resins have been known as such a coating material (for example Japanese Patent Laid-Open No. Sho 52-154639, Japanese Patent Laid-Open No. Sho 54-35735 and the like).
Japanese Patent Laid-Open No. Sho 52-154639 discloses that polypropylene resins and the like are heated to be molten in suitable solvents and the resulting molten resins are spray-coated to carrier core materials to obtain carriers particles of which surfaces are coated with polypropylene resins.
Japanese Patent Laid-Open No. Sho 54-35735 discloses that coating material powders are stuck to surfaces of carrier particles and heated at melting temperature of the coating material or more to be fixed, whereby coated carriers are obtained.
However, the carrier particles, of which surfaces are coated with polyolefinic resins as above described, have shown disadvantages in that the adhesion of coating layers to carrier particles is poor and a durability is inferior. For example, if the copying process is repeated, the coating layers are separated. In addition, the above described methods have shown a disadvantage in that, for example, the control of layer-thickness is not easy.